German Pat. App. No. P2201631.5 discloses an extruderhead of divided construction for connection to two superposed screw extruders to form shapes of different compounds. The extruderhead is divided into two planes which are inclined upwardly and downwardly from the horizontal extrusion plane to the cylinders of the extruders. The extruderhead is composed of three parts of which the middle part is fast with the screw presses while the other two parts are hinged so that the two outer parts are held together during operation of the extruder by two horizontally slidable clamps which have clamping faces that are slightly inclined to the horizontal and which support opposed clamping faces of the hinged parts. The two outer parts lie against supporting faces of the middle part which are inclined with respect to the horizontal with an inclination opposite the inclination of the parting plane. This extruderhead is characterized by being easy to open and also easy to clean. The flow channels of the extruderhead lie wholly in the parting plane so that material remaining in the channels can be easily removed. In this extruderhead there are no channels in the form of tubing.
An extruderhead of this kind can be designed for a group of products which are of similar form. It can also be designed to produce other groups of products. However, there are disadvantages which become greater with greater differences in the profile cross section. These disadvantages are the following. With small profiles an undesirable pressure builds up in at least one of the extruderhead parts which by reason of the relatively large material guiding faces produces a high load force on the head. It forms unfavorable slow points which can lead to temperature rise and particularly to prevulcanization of the material to be extruded. In some parts of the flow channel material can dwell for a longer time. This results at elevated temperatures which can lead to prevulcanization and heterogeneousness in the mixture. When the portions of material which have been retained at higher temperature in unfavorable locations in the flow path are freed after a period of time and again enter in the stream of material they cause noticable homogenity disturbing characteristics in the product.
These disadvantages in products which on account of their profile cross section cannot satisfactorily be produced with an extruderhead of this kind narrows down the range of products that can be produced with this kind of extrusionhead. For this reason it is necessary to use several extruderheads for one on the same extruder unit in order to produce a wide product line. The initial cost of several extruderheads is considerable. Moreover, production time is lost by reason of the installation time involved in changing the extruderheads.
In the production of particular flat profiles there is also the disadvantage that the screws of the extruders cannot be pulled out through the opened extruderhead because the walls of the flow channels are so formed that they are in the way of pulling out the screws. This greatly increases the difficulty of cleaning or of changing over the extruder apparatus.